The present invention relates to an image forming apparatus which employs recording sections arranged in an array form and conducts exposure on a photosensitive material moving relatively to the recording sections to form an image.
There has been a technology to record color images on a color silver halide photosensitive material by the use of light sources arranged in an array form (hereinafter referred to as "array light source"). With regard to the technology, there has been suggested an apparatus employing, for example, a print head having a vacuum fluorescent tube light source called VFPH (Vacuum Fluorescent Print Head). A vacuum fluorescent tube light source (VFPH) of this kind has special features that high luminance can easily be obtained, response is quick and a light source is of a thin type. As a phosphor used in this case, zinc oxide phosphor (ZnO:Zn) is selected mainly from the viewpoint of durability.
The vacuum fluorescent tube light source (VFPH) has therein a light emitting dot row wherein light emitting elements are arranged in an array of a row or plural rows on a base plate in a vacuum receptacle, the cathode stretched above the light emitting dot row, and a grid which covers at least a part of the base plate in the vicinity of the light emitting dot row, and it conducts exposure on a photosensitive material moving relatively to a recording section by using the recording section equipped with an image focusing optical system that forms an image outside the vacuum receptacle from light from a light emitting dot and is equipped with a driving element for a light emitting dot.
However, when conducting exposure on a photosensitive material by the use of an optical recording head equipped with light emitting dots arranged in an array form, it is necessary, for preventing dispersion of light sources of the optical recording head, to make corrections of an amount of emitted light in accordance with each phosphor.
Due to the short focal depth, it was impossible, in the conventional optical recording head, to correct a quantity of light sufficiently through photometry of a quantity of light alone. Therefore, a quantity of light has been corrected through densitometry of samples of exposed photosensitive materials. However, it has been necessary to repeat correction by densitometry, because of the short focal depth of an optical recording head and an influence of light emission of adjoining pixels in densitometry caused by blurring in photosensitive materials. Further, when correcting a quantity of emitted light through densitometry, density is changed also by shifted focus (image forming point), and when conducting exposure while moving an optical recording head and a photosensitive material, the quantity of light corrected once is changed by fluctuation of focus to cause dispersion, which has been a problem.
In the case of an optical recording head equipped with light emitting dots which are arranged in a form of an array, in particular, adjoining pixels are influenced by light emission to cause unstable quantity of light, thereby, density difference between adjoining pixels is caused, and a quantity of light is lowered when light emission is continued for a long time, which have been specific problems.